Thermochemistry on the Complex of Erbium Perchlorate with L-α-Glutamic Acid [Er2(L-Glu)2(H2O)6](ClO4)4·6H2O(s)
Abstract
A coordination compound of erbium perchlorate with L-α-glutamic acid, [Er2(Glu)2(H2O)6](ClO4)4·6H2O(s), was synthesized. By chemical analysis, elemental analysis, FTIR, TG/DTG, and comparison with relevant literatures, its chemical composition and structure were established. The mechanism of thermal decomposition of the complex was deduced on the basis of the TG/DTG analysis. Low-temperature heat capacities were measured by a precision automated adiabatic calorimeter from 78 to 318 K. An endothermic peak in the heat capacity curve was observed over the temperature region of 290–318 K, which was ascribed to a solid-to-solid phase transition. The temperature Ttrans, the enthalpy ΔtransHm and the entropy ΔtransSm of the phase transition for the compound were determined to be: (308.73±0.45) K, (10.49±0.05) kJ·mol−1 and (33.9±0.2) J·K−1·mol−1. Polynomial equation of heat capacities as a function of the temperature in the region of 78–290 K was fitted by the least square method. Standard molar enthalpies of dissolution of the mixture [2ErCl3·6H2O(s)+2L-Glu(s)+6NaClO4·H2O(s)] and the mixture {[Er2(Glu)2(H2O)6](ClO4)4·6H2O(s)+6NaCl(s)} in 100 mL of 2 mol·dm−3 HClO4 as calorimetric solvent, and {2HClO4(l)} in the solution A' at T=298.15 K were measured to be, ΔdHm,1= (31.552±0.026) kJ·mol−1, ΔdHm,2= (41.302±0.034) kJ·mol−1, and ΔdHm,3= (14.986±0.064) kJ·mol−1, respectively. In accordance with Hess law, the standard molar enthalpy of formation of the complex was determined as ΔfH⊖m = − (7551.0±2.4) kJ· mol−1 by using an isoperibol solution-reaction calorimeter and designing a thermochemical cycle.
